After my '82 Stang killed it's second battery in three years, I took the car to an auto electric shop in town. I asked for an alternator upgrade, but he discovered that the Autozone alternator had the wrong pulley on it, so it was not turning fast enough at idle to charge the battery. Since I rarely drove it, and usually only around town and/or at night, idling with headlights, brake lights, radio, etc. killed the battery. Since he installed the correct pulley I have had no problems.
Gregg
2001 Proton Yellow #1379